Whether his actions would be warranted, or legal, is also hotly debated.

Trump renewed his threat Thursday, saying he would almost “definitely” declare a national state of emergency if a deal isn’t reached with Democrats in Congress to end a stalemate over funding a U.S.-Mexico border wall. The federal government shutdown caused by the dispute is now in its 20th day.

“If this doesn’t work out, probably I will do it,” he said in comments to reporters before leaving the White House for a trip to the border.

Trump made the same threat over the weekend.

Invoking a state of emergency effectively enhances the president’s executive powers by creating exceptions to the usual rule of law. This authority is intended for the president to quickly respond to matters deemed a public threat. In such times, ordinary laws and civil protections no longer apply.

The New York Times described Trump using his emergency authority to build a border wall as an “extraordinarily aggressive move,” adding that it would be, “at a minimum, a violation of constitutional norms.”

U.S. leaders have declared national emergencies for decades, with 58 of them on the books since 1979 when President Jimmy Carter signed an order to block Iranian government property from entering the country, according to Pacific Standard. Although Carter signed the order in response to the Iran hostage crisis, it remains in effect and was extended in November 2018.

In fact, 31 declared national emergencies remain in effect, according to the Brennan Center for Justice at New York University. These include former President George W. Bush’s Proclamation 7463 after 9/11, issued by “Reason of Certain Terrorist Attacks.”

There are several national emergencies ongoing from President Barack Obama. They include the order “Blocking the Property of Certain Persons Engaging in Significant Malicious Cyber-Enabled Activities.”

The Brennan Center considers some powers afforded to the president in national-emergency cases as “easily exploitable,” such as if a president were to suspend bans on testing chemical and biological weapons on people. The president could also use his powers to control internet traffic, as well as voter databases, the Atlantic reported.

Three times Trump has invoked the National Emergencies Act, including an order to sanction people over their alleged involvement in election tampering, Politico reported. It’s been criticized as overly broad.

But if the president declares a state of emergency, “More is at stake here than the outcome of one or even two elections,” reports the Atlantic. “Trump has long signaled his disdain for the concepts of limited presidential power and democratic rule.”